Sintered article and method of making the same



atented July 14, W42

SIZNTIEREHB AR'EHCLE METHOD OF MAKITNG THE SAME No Drawing. Application September 6, 1940, Serial No. 355,609

4 Claims.

This invention relates generally to powder etallurgy and more particularly to powders rmed of brittle copper-tin alloys and the usage the formed powders in the formation of sinecl bronze articles. it is well known to form articles such as bronze shings and other shapes from powdered copand powdered tip which are mixed together th some graphite (with suitable binders if deed), briquetted and then sintered. The powred copper available on the market for this rpose is expensive and costs considerably more 5.11 the market price of ingot copper. The no applies to the powdered tin. Dne important object of this invention is to luce the cost of sintered bronze articles. another object of this invention is to introduce of the tin and a portion of the copper relred in the production of sintered bronze arles in the form -of a. brittle copper-tin alloy it is readily and economically comminuted'or mud to the size of powder required. [t is also an object of this invention to provide economical method of making briquetted and .tered bronze articles that are stronger than ;icles made by briquetting and sintering under iilar conditions a mixture of copper powder d tin powder. Still another object of the present invention to provide an economical method of producing alloy powder of copper and tin that is espelly adapted for use in the fabrication of sined articles. Dther objects and advantages of my invention 1 become more apparent as the description )ceeds. In accordance with a preferred embodiment of invention, I provide a molten copper-tin alof such composition that the solidified alloy quite brittle and friable, and hence may be ldily comminuted or ground to any desired B. An alloy composed of about forty per cent and the balance substantially all copper has a necessary friability and at the presenttime preferred. However, greater amounts of tin ,y be used to produce alloys having the desired ability to permit easy powdering. In general s contemplated that about thirty-five to sixty 7 cent of tin and the balance substantially all ip'er may be employed. ['he copper-tin alloy mat be cast into suitle shapes and thereafter broken up in a suitle grinding or ball mill to the size of powder iiled. The particular size in any case will dead on the use, but ordinarily it will be of a e such that it will all pass through a 100 mesh eon. In general, powde'r sizes on the same ler as thosen'ow. employed in making articles m briquetted and sintered powdered materials a usable. The copper-tin alloy powder is much less costly than equivalent amounts of copper and tin as separate or non-alloyed powders. This is due largely to the ease with which the alloy material is broken up into powder as compared with the cost of powdering copper and tin separately.

. In the formation of sintered and briquetted bronze articles in accordance with. a preferred embodiment of the invention all of the tin required in the final article is introduced in the form of the brittle copper-tin alloy powder. The required amount of the copper-tin alloy powder is then intimately mixed with copper powder and a small amount of graphite. The powder mixture is then compressed or briquetted into the form desired and thereafter sintered. Brigas 01' gases.

The copper-tin alloy powder in addition to reducing the cost of the sintered article by a less costly source of the tin that is necessary and by a less costly source of a portion of the copper required, also assists in making a stronger sin-' tered material than where separate copper and tin powders are used. This is due to the fact that where the tin is supplied in the form of the copper-tin alloy powder no voids, such as produced during sintering. In the present invention as the sintering operation proceeds, some of the tin migrates from the copper-tin alloy particles into the copper particles, leaving behind the copper-tin alloy particles of reduced tin content. This results in a sintered article having less discontinuity of structurethan where separate copper and tin powders are employed. The migration of the tin from the regions of high tin content into those of no tin content increases the strength of the particles or regions low in tin and eliminates the brittleness from the par-' ticles which were originally high in tin. The difiusion can be carried out to the point where the composition and structure are uniform throughout. A ductile material or article is thus produced that is stronger and more homogeneous than an article of similar analysis made by briquetting and'sintering under similar condiatmosphere containing carbon monoxide.

,In addition to the above described advantages resulting from forming bronze articles by a mixture of copper and copper-tin alloy powders, it appears that the frictional or stripping pressures are substantially lower than with briquettes formed of a mixture of copper and tin powders. Lower stripping pressures mean less wear of the dies used in the briquetting operation and permit articles of greater lengths to be briquetted.

For illustrative purposes the following specific examples of procedure in accordance with the invention may be given.

Twenty-five parts of an alloy powder composed of forty per cent tin and the balance copper was intimately mixed with seventy-five parts of copper powder, briquetted under a pressure of 50,000 pounds per square inch, and thereafter sintered at a temperature of 1500 F. in a non-oxidizing The powders were of a size such that all would pass through a 150 mesh screen and about eighty-five per cent through a 200 mesh screen. A strong sintered bronze article was produced.

In another case ten parts of a nickel-silicon alloy composed of twenty-eight per cent silicon, about two per cent iron and the balance copper, were thoroughly mixed with five parts of the forty per cent copper-tin alloy powder and eighty-five parts of copper powder. The mixture was briquetted under a pressure of 50,000 pounds per square inch and sintered under non-oxidizing conditions at, a temperature of 1700 F. The powders were of a size such that all would pass through a 150 mesh screen and about-eighty-five per cent through a 200 mesh screen. The sintered article had a strength of about 40,000 pounds per square inch and had good properties as regards score resistance.

In some cases it may be desirable that the copper-tin alloy'powder be of a difi'erent size than the copper powder. In making articles by j briquetting and sintering it is often desirable to provide a certain amount or proportion of the powder of avery fine size. Due to the ease which the copper-tin alloy material can be broken up into a very fine powder, the alloy powder may conveniently supply the amount of extremely fine powder required.

Various changes and modifications of the preferred embodiments of my invention described herein may be made without departing from the principles of my invention and I do not intend to limit the patent granted thereon except as necessitated by the prior art.

I claim:

l. The method of making a briquetted and sintered bronze article which comprises; forming a copper-tin alloy powder consisting of to 60% tin and the balance substantially all copper; mixing a relatively small amount of said copper-tin alloy powder suflicient to provide the required tin content in the finished article, with copper powder; briquetting the mixture of the copper-tin alloy powder and the copper powder; and sintering said briquetted powder mixture at a sintering temperature below the melting point of the copper powder and at least as high as the minimum temperature necessary to fuse entirely the copper-tin alloy powder and for a time sufiicient tocause migration of tin from the coppertin alloy powder particles into the copper powder particles until .the tin content in the copper-tin alloy powder particles is lowered to the po where they become ductile to thereby form ductile, sintered bronze article consisting of cc per and tin and having less discontinuity structure and greater strength than sintei bronze articles of similar analysis formed briquetting and sintering a mixture of cop; powder and tin powder.

2. The method of.making a briquetted a sintered bronze article which comprises, for] ing a brittle copper-tin alloy material containi 35% to 60% tin and the balance substantia all copper, forming a powder of said copper-' alloy of a size such that it will at least p2 through a 100 mesh screen, mixing a relativt small amount of said copper-tin alloy powc suificient to provide the amount of tin desir in the bronze with the necessary amount of cc per powder, compressing said mixture of powde under high pressure into the shape desired, a sintering said briquette at a temperature about 1500 F. ina non-oxidizing atmosphe and for a time sufficient to cause migration the tin from the copper-tin alloy particles to t copper particles and to form a strong ductile si tered bronze article of homogeneous structt throughout.

3. The method of making a briquetted a: sintered article which comprises forming a br; tle copper-tin alloy powder containing 35% tin and the balance substantially all copp mixing a relatively small proportion of said co per-tin alloy powder with a relatively large pr portion of other metallic powder to provide of the'tin desired in the final article, briquetti: said powder mixture, and sintering said briquei at a sintering temperature at least as high the minimum temperature necessary to provi a molten component in the copper-tin alloy po der and for a time suiiicient to cause migrati1 of the tin into the other metallic powder particl until the tin becomes substantially uniform diflfused throughout the article whereby a stror ductile sintered article of homogeneous structu is produced.

4. The method of making a briquetted a] sintered bronze article which comprises, for: ing a brittle copper-tin alloy containing abo 4.0% tin and the balance substantially all coppr powdering said brittle copper-tin alloy to a si such that it will pass through a 150 mesh scree mixing about twenty-five parts of said briti copper-tin powder with about seventy-five par of copper powder of a size such that it will pa through a 150 mesh screen, all of the tin in ti final article being supplied by the brittle coppe tin alloy powder, briquetting said powder mi: ture under a pressure of around 50,000 poun per square inch, and sintering said briquette a temperature of about 1500 F. in a non-oxidi ing atmosphere until tin from the copper-t alloy powder particles has diffused substantial uniformly through the copper particles and strong, ductile bronze article consisting of abo copper and 10% tin is produced haviz greater strength and less discontinuity of stru ture than sintered bronze articles of simil: analysis formed by briquetting and sinteriz under similar pressure and temperature 00nd tions a mixture of copper powder and tin powde ALFRED L. BOEGEHOLD. 

